Method of feeding flat mail for separation by suction of material input

ABSTRACT

The invention relates to a method for the steady feeding of flat items for separation by suction of material input into a distribution unit by using a feeding device, preferably comprising a separating blade and a conveyor belt underneath it. In accordance with the invention, the thickness of the pulled-off items is measured within a main control circuit (HR). The feeding device conveys the item stack (SS) by the amount of this thickness in the direction of the suction separation system. In a static correction control circuit (KR), the stack pressure is measured outside of the suction separation system and is adjusted via the movement of the feeding device within the limits of the permissible stack pressure range.

BACKGROUND OF THE INVENTION

The invention relates to a method for feeding flat items for separationby suction of material input into a distributing unit by using a feedingdevice, preferably comprising a separating blade and a conveyor beltarranged underneath.

The items are fed to the system for separation by suction by way of theseparating blade and the conveyor belt arranged underneath. If thepressure in the item stack is high, there is danger that two articlesare pulled off at the same time as a result of the frictional forcebetween the individual items. On the other hand, if the item stack isnot compact enough, the throughput is relatively low. The individualitems additionally can tip over, thereby worsening the pull-offbehavior. For that reason, a certain stack pressure range must bemaintained in the separating region.

A suction device is installed underneath perforated friction belts toachieve an increase in the frictional force between the first item andthe friction belt for the separation system. Consequently, the stackpressure is up to now checked with sensing levers and position sensors,which switch the separating blade and the conveyor belt underneath andthus also the item feeding device on and off via a two-position control.The sensing levers here are located in the region where the items aresuctioned out. The sensing levers are consequently actuated by anexcessively high stack pressure as well as by items that are suctionedin. The operation for controlling the stack pressure thus is not definedclearly. Thus, suctioned-in postcards can stop the separating blade andthe conveyor belt underneath via the sensing levers as soon as a gapforms in the stack of items in front of the pull-off location. After allthe items in front of this gap have been separated, the feeding devicemust move the item stack at least by the amount of the gap in thedirection of the pull-off point until further items can be separated. Asa result, larger gaps form in the conveying section, following theseparation, and these worsen the throughput. In those cases, there isalso an increased tendency to pull off two items at the same time, owingto the briefly increased stack pressure.

A further disadvantage arises from the fact that the sensing levers arespring-weight-systems, which vibrate strongly during the separation bysuction.

SUMMARY OF THE INVENTION

It is the object of the invention, to create a method for feeding flatitems to the system for separation by suction of material input, whichmethod eliminates the shortcomings in the state of the technology, sothat a steady feeding and separation of the item stacks is achieved.

The advantage of the solution according to the invention is that itremoves the undefined condition during the control of the suctionseparation feeding, during which a feeding stop could be triggered by anexcessively high stack pressure as well as a single item suctioned in.

In one advantageous embodiment, the thickness of the pulled-off item isdetermined via the deflection of a swivelling roller, by means of arotary potentiometer. In a further advantageous embodiment of theinvention, the stack pressure is measured at the feeding device via aspring-mounted and damped separating blade and position sensors,arranged on both sides of the separating blade.

The invention is explained further with an example and with the aid ofthe drawings, which show in:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A basic diagram of a device for executing the method according tothe invention;

FIG. 2 A basic diagram of a device for executing the method usedheretofore.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 2 shows that the item stack SS is fed to the system for separationby suction with the aid of the separating blade TM and the conveyor beltUB underneath it. In order to increase the frictional force between thefirst item and friction belts RR for pulling off the items, these beltshave a perforated design with a suction device SW located underneath thefriction belts RR. Owing to the vacuum in the suction device SW, thefront item is pulled toward the friction belts RR.

To achieve an even stack pressure in the item stack, the stack iscontrolled via the sensing levers FH and the position sensors PS, whichturn the separating blade TM and the conveyor belt UB underneath it onand off via a two-position control. A feeding stop can also be triggeredby a suctioned-out item, even though there is a gap in the item stack SSafter this item.

The solution according to the invention, based on FIG. 1, provides thatthe thickness of each pulled-off item is measured with a rotarypotentiometer DP at a swivelling roller SR in the transfer region. Therigidity of the spring for swiveling roller SR is selected high enough,so that stronger vibrations can be ruled out and the dynamic influencetherefore is insignificant. The separating blade TM or the conveyor beltUB underneath it track the respectively measured thickness in a maincontrol circuit HR.

However, possible errors in the thickness measuring can add up whenusing this control principle. Also, the system does not detect whetherthe item stack SS has the right stack pressure from the start. The stackpressure is therefore monitored and corrected in a correction controlcircuit KR.

This control circuit can remain on static control, owing to the fewreadjustments that are required.

In the cited example, the stack pressure is controlled with the aid oftwo position sensors S1 and S2, which are positioned to the left andright of a spring-mounted separating blade TM. If the stack pressure istoo high, the separating blade TM approaches the position sensor S1which then switches. If the stack pressure is too low, the positionsensor S2 switches. The separating blade TM is damped, so that the twoposition sensors S1 and S2 do not react to short-term pressurefluctuations in the item stack SS. The items fit better against thefriction belt RR because the presently used sensing levers FH areomitted. This improves the pull-off behavior considerably.

What is claimed is:
 1. A method for feeding flat items for separation bysuction of material input into a distribution unit through a suctionseparation system, by using a feeding device comprising the stepsof:measuring a thickness of a pulled-off item in a main control circuittransporting an item stack by the amount of the measured thickness inthe direction of the suction separation system; measuring a stackpressure outside of the suction separation system in a static correctioncontrol circuit; and adjusting the stack pressure by means of moving thefeeding device within the limits of a permissible stack pressure range.2. A method according to claim 1, wherein the step of measuring athickness further comprises:deflecting a swiveling roller to measure thethickness of the pulled-off items.
 3. A method according to claim 2,wherein the step of measuring the thickness further comprises:measuringthe deflection of the swiveling roller with a rotary potentiometer.
 4. Amethod according to claim 1, wherein the step of measuring the stackpressure occurs at the feeding device.
 5. A method for feeding flatitems for separation by suction of material input into a distributionunit through a suction separation system, by using a feeding device,comprising the steps of:measuring a thickness of a pulled-off item in amain control circuit; transporting an item stack by the amount of themeasured thickness in the direction of the suction separation system;measuring a stack pressure outside of the suction separation system in astatic correction control circuit the stack pressure being measured viaa spring-mounted and damped separating blade and position sensorsarranged on both sides of the separating blade; and adjusting the stackpressure by means of moving the feeding device within the limits of apermissible stack pressure range.
 6. A method for feeding flat items forseparation by suction of material input into a distribution unit througha suction separation system, by using a feeding device, comprising thesteps of:measuring a thickness of a pulled-off item in a main controlcircuit; transporting an item stack by the amount of the measuredthickness in the direction of the suction separation system; measuring astack pressure outside of the suction separation system, at the feedingdevice, in a static correction control circuit the stack pressure beingmeasured via a spring-mounted and damped separating blade and positionsensors arranged on both sides of the separating blade; and adjustingthe stack pressure by means of moving the feeding device within thelimits of a permissible stack pressure range.